Industrial Maintenance Solutions

AN OVERVIEW OF HYDRODYNAMIC BEARINGS, THEIR DEFINITION, THEORY OF OPERATION AND TROUBLESHOOTING TIPS. BY AMR HATEM RASHED. Hydrodynamic bearings (also known as fluid film bearings) are often deployed as journal bearings. As such, they come in several types, including radial tilting pad bearings, thrust bearings for axial displacement and journal sleeve bearings. Journal sleeve bearings are typically used in low-speed and low-friction applications while radial tilting pad bearings are used for high-speed applications due to the high amplitude of vibrations. Thrust bearings, on the other hand, are generally employed for axial displacement in high-speed applications as they contain tilting pads that support high-thrust loading of rotors. Pivoted shoe journal bearing Pivoted shoe thrust bearing Frictionless support The journal bearing has several functions. It acts as frictionless support for the rotor while it is rotating. It cools down the rotor by transferring the heat energ...

Residual magnetism in high-speed machinery accounts for many previously unexplained machinery failures. In particular, the deterioration of bearings, seals, gears, couplings and journal s has been attributed to electrical currents in machinery. Often, such trains or machinery groupings contain no components with electrical windings or intended magnetism, i.e., no motors or generators. The evolution of turbine and compressor systems towards high speeds and massive frames is acknowledged as the cause for a new source of trouble from magnetic fields. An electrical generator converts mechanical power to electrical power through magnetic fields. A conventional generator rotor is essentially a magnet that is rotated in such a manner that its magnetic field flux passes through coils of windings. This produces an electrical voltage and power in the windings. A turbine, compressor, or any other rotating machine that is magnetised behaves much the same way. The magnetic steel parts provide a...

BY AMIN ALMASI. There are many reasons for turbomachinery problems and failures. Resonance, for example, is often overlooked.  Rotating parts and components such as impellers and blade rows could be in resonance with any excitations generated by turbomachinery. Resonances for the first and second natural frequencies can be dangerous. Generally, there could be numerous cases of resonance. The second natural frequency of a rotating component, in one example, proved to be almost exactly an integer multiple of the first natural frequency. This led to excitation and operational problems. Fluid-induced vibration, oscillatory changes of fluid pressure, and turbulent flow (vortex formation) might also cause high vibration or even failure.  Fatigue, too, is often a root cause in failures of rotating parts. Individual stress amplitudes should be analyzed to ensure associated components will not fail due to different forms of fatigue such as high-cycle fatigue (HCF) and low-cycle fatigue...

BY MICHAEL FORSTHOFFER. In the last 10+ years there has been a significant increase in the technology and instrumentation used on dry gas seal systems to monitor the condition of the seals. Most notable has been the call to monitor secondary seal condition – there have been significant failures of the secondary seal without any issue with the primary seal. The majority of these failures have been due to oil migration across the separation seals. As the oil is not drained out, it accumulates around the secondary seal, fills the grooves, and causes the secondary seal faces to contact. There are various approaches to monitoring secondary seal condition. Probably the most beneficial is utilizing a back pressure control valve in the primary vent (Figure). Figure: Using a back pressure control valve in the primary vent as part of the monitoring of secondary seal condition in a dry gas seal. This sets the primary vent at a pressure below the primary seal gas supply pressure, but high en...

BY TALAL AL-RASHIDI & HAMAD K. AL-RUZIHI T wo multistage 16,000 HP electrical motors are used to drive two onshore gas compressors feeding a gas plant commissioned in 1984 (Figure 1). Figure 1: Onshore compressor skid . These compressors needed to produce gas at a higher capacity. Unfortunately, the existing units were unable to meet the new demand. One option considered was purchasing and installing an additional compressor. Engineers also evaluated the possibility of utilizing the available capacity of adjacent o ff shore compressors. Although onshore and o ff shore gas compressors are located on the same platform and discharge to a common header, they were designed to process di ff erent gas molecular weights due to separate feeds for onshore and o ff shore units (Figure 2). Figure 2: Compressor flow schematics. The challenge was to ensure that o ff shore compressors could handle not only the new capacity but the new gas conditions. As the plant receives gas from two associa...

Thermal growth, as used in the field of machinery alignment, is machine frame expansion resulting from heat generation. The generation of heat, of course, is caused by operational processes and forces. Materials subjected to temperature changes from heat generation will expand by precise amounts defined by their material properties. In turbomachinery, thermal growth results from the temperature differences occurring between the at-rest and running conditions. Generally speaking, the greater the temperature difference, the greater the thermal growth. The magnitude of the growth can be calculated from three variables: ∆ T (temperature difference) C   (coefficient of thermal expansion) L    (distance between shaft centerline and machine supports) When machinery begins to generate heat, the temperature difference between at-rest and running conditions will cause thermal expansion of the machine frame, thereby bringing about the movement of the shaft centerlines. This can...